The effects of attention-deficit/hyperactivity disorder (ADHD) can extend well beyond childhood, according to the latest research.

In the largest study of its kind, researchers at Boston Children’s Hospital and Mayo Clinic found that close to a third of children with ADHD — 29.3% — still have the disorder as adults, along with an increased rate of other psychiatric problems. “We have trivialized this condition,” says lead author Dr. William Barbaresi. “We need to recognize that this is a chronic health problem that often persists into adulthood.”

Previous estimates of the rate at which ADHD persists into adulthood had ranged widely, from 6% to 66%, but those studies relied on small groups of children. Barbaresi and his colleagues identified 379 cases of ADHD in the 5,718 children born during a six-year period from 1976 to 1982 in Rochester, Minn. Between 7% to 9% of the Rochester kids developed ADHD, which is consistent with current national estimates of 7.5%. Decades later, they were able to track down and enlist 62% of those now-adults — 232 people — to participate in the research.

Of the third who still had ADHD at age 27, 81% had at least one additional psychiatric disorder and 47% of those who no longer had ADHD had at least one other psychiatric diagnosis, according to the study published in the journal Pediatrics. The findings suggest that ADHD may frequently occur with other mental health disorders, and may serve as a marker for these condition. “That group with ADHD is at highest risk for having additional mental health problems,” says Barbaresi, who is director of the Developmental Medicine Center at Boston Children’s Hospital and an associate professor of pediatrics at Harvard Medical School. “We have to stop trivializing ADHD as just another childhood behavior problem. The nature and duration of this study show we have to recognize it as a chronic serious health problem that deserves a lot more attention than it has received.”

It’s not that the condition isn’t being addressed adequately, or that doctors, parents and teachers are not aware of the condition: they certainly are, since education and awareness about ADHD has increased in recent decades, even contributing to a rise in diagnoses. In that time, schools and parents have tried to improve learning environments to help children who have difficulty concentrating so they can get more from their education in the classroom. Barbaresi argues, however, that the legacy and long term implications of an ADHD diagnosis haven’t really been considered and studied adequately, since most doctors tend to think of the condition as one that primarily affects children that they tend to outgrow once they reach adulthood. The need for attention is even greater considering that the study also found a connection between ADHD and suicide. While the absolute number of deaths in the adults who still have ADHD is low, the statistical difference is significant: children with ADHD were nearly five times more likely to die from suicide than other people in the study group.

Of the seven deaths in the twenty- and thirty-something adults who had a history of chilhood ADHD, five were associated with psychiatric and substance abuse problems. “We have to pay attention to the things that go with ADHD,” says Barbaresi.

In addition, data from this same group of study participants showed that more than 60% of kids with ADHD have a learning disability and develop at least one additional mental-health problem while they’re still children. Yet insurance companies are reluctant to authorize additional assessments that may detect and treat these conditions. “If a child gets diagnosed with ADHD, we want to do a comprehensive psychological assessment to see if the child has undiagnosed disorders because we know these kids are at risk,” says Barbaresi. “But insurance won’t pay.”

That’s in stark contrast to the way that children are evaluated for other medical conditions, such as diabetes. “We know they’re at risk for developing kidney and eye problems so they’re regularly assessed for those issues. We don’t wait until a child has renal failure or loses his eyesight,” says Barbaresi. “But with childhood ADHD, we can’t get authorization to do these assessments until it’s already happened.”